In conventional wireless communication apparatuses having transmission and reception functions, a transmission system and a reception system are generally provided independent of each other in a radio unit. On the other hand, it has been attempted to accomplish simplification, decrease in size, and reduction in cost of the radio unit by sharing all or a part of the transmission system and the reception system.
Here, in order to use a frequency converter for performing frequency conversion of signals in the wireless communication apparatuses in common to the transmission system and the reception system, it is necessary to perform the frequency conversion between an intermediate frequency signal (hereinafter, referred to as IF signal) and a radio frequency signal (hereinafter, referred to as RF signal) in two ways.
An example of a conventional bidirectional frequency converter is disclosed in a document, entitled “Fundamental and Development of Microwave Semiconductor Circuit,” written by Honjyo Kazuhiko, supervised by Konishi Yoshihiro, and made by THE NIKKANKOGYO SHIMBUN, LTD. p. 196-197. FIG. 20 is a circuit diagram illustrating an example of the bidirectional frequency converter disclosed in the document entitled “Fundamental and Development of Microwave Semiconductor Circuit.”
In FIG. 20, when the bidirectional frequency converter converts an RF signal into an IF signal in frequency, the RF signal input to terminal 601 is input to diode bridge 606 through transformer 602 and a local oscillation signal (hereinafter, referred to as LO signal) is input from terminal 603 to diode bridge 606 through transformer 604. Then, the bidirectional frequency converter mixes the signals by the use of non-linearity of a diode to generate an IF signal and outputs the generated IF signal through terminal 605. When the bidirectional frequency converter converts the IF signal into the RF signal in frequency, the IF signal is input to terminal 605 and is mixed with the LO signal input from terminal 603 by diode bridge 606 to generate a RF signal. Then, the bidirectional frequency converter outputs the generated RF signal from terminal 601 via transformer 602. In the configuration shown in FIG. 20, since a diode is used as a non-linear element and diode bridge 606 has a symmetric circuit configuration, the RF signal and the IF signal can be converted in frequency into each other in two ways.
Another example of the conventional bidirectional frequency converter is disclosed in Japanese Patent No. 3258791. FIG. 21 illustrates a configuration of an example of a communication apparatus having the bidirectional frequency converter disclosed in Japanese Patent No. 3258791.
FIG. 21 is a diagram illustrating an operation of communication apparatus 700 at the time of reception. In FIG. 21, antenna 701 is used in common to reception and transmission and is connected to switch 702. Switch 702 connects antenna 701 to reception signal amplifier 703 and inputs a reception RF signal received by antenna 701 to reception signal amplifier 703. An output terminal of reception signal amplifier 703 is connected to switch 704. Switch 704 connects reception signal amplifier 703 to frequency converter 705 and inputs the reception RF signal amplified by reception signal amplifier 703 to frequency converter 705.
LO signal oscillator 708 generates an LO signal and the generated LO signal is input to frequency converter 705 through amplifier 706. Frequency converter 705 mixes two input signals of the reception RF signal and the LO signal to generate a reception IF signal. Switch 707 connects frequency converter 705 to reception signal output terminal 709 and outputs the reception IF signal generated by frequency converter 705 to reception signal output terminal 709.
Up to now, the operation of communication apparatus 700 at the time of reception has been described. At the time of transmission, the circuit configuration is changed so that switch 704 connects transmission signal input terminal 710 to frequency converter 705, switch 707 connects frequency converter 705 to transmission signal amplifier 711, and switch 702 connects transmission signal amplifier 711 to antenna 701. In the configuration shown in FIG. 21, communication apparatus 700 can use one frequency converter 705 in common to reception and transmission, by changing a signal path in transmission and reception by the use of switches.
Another example of the conventional bidirectional frequency converter is disclosed in Japanese Patent No. 3369396. FIG. 22 is a diagram illustrating a configuration of an example of the bidirectional frequency converter disclosed in Japanese Patent No. 3369396.
In FIG. 22, terminal 801 to which a reception RF signal is input and terminal 802 to which a transmission IF signal is input are connected to adder 803. Adder 803 outputs an added signal of the reception RF signal and the transmission IF signal. The added signal is input to frequency converter 804 and is mixed with an LO signal input from terminal 805 to generate a reception IF signal and a transmission RF signal. An output terminal of frequency converter 804 is connected to buffer amplifiers 806 and 807. Buffer amplifier 806 amplifies the generated reception IF signal and outputs the amplified reception IF signal to terminal 808 and buffer amplifier 807 amplifies the generated transmission RF signal and outputs the amplified transmission RF signal to terminal 809.
In the configuration shown in FIG. 22, one frequency converter 804 can be used in common to reception and transmission, by using adder 803 at the input side of the frequency converter and using buffer amplifiers 806 and 807 at the output side thereof.
However, in the conventional configuration disclosed in the document entitled “Fundamental and Development of Microwave Semiconductor Circuit,” since a diode is used at a non-linear element, there is a problem that loss of power occurs at the time of frequency conversion, thereby causing conversion loss.
In the conventional configurations disclosed in Japanese Patent No. 3258791 and Japanese Patent No. 3369396, since the reception RF signal and the transmission IF signal are input to the same input terminal of the frequency converter and the reception IF signal and the transmission RF signal are output from the same output terminal, the input terminal and the output terminal must be matched with both frequency bands of the IF signal and the RF signal and thus a matching circuit is complicated. In addition, there is a problem that constituent components other than the frequency converter, such as switches for switching a signal path, an adder, and buffer amplifiers, are necessary for transmission and reception.